Display apparatus and driving device for displaying

ABSTRACT

A display drive circuit for outputting a gray scale voltage according to display data includes a generation circuit generating gray scale voltages of a plurality of levels, and a selection circuit which selects a gray scale voltage according to the display data. When the number of colors to be displayed is small, the generation circuit decreases a current flowing into an internal circuit which generates a gray scale voltage of an intermediate level other than two gray scale voltages of a gray scale voltage of the most lowest level and a gray scale voltage of the most highest level among the gray scale voltages of the plurality of levels, and the selection circuit selects the gray scale voltage according to the display data from the most lowest level gray scale voltage and the most highest level gray scale voltage which are generated.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 10/918,379, filedAug. 16, 2004, which is a continuation of U.S. application Ser. No.10/161,638, filed Jun. 5, 2002, now U.S. Pat. No. 6,781,605, the subjectmatter of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a display apparatus having a displaypanel in which display pixels are arranged in matrix and a drivingdevice for displaying adapted to deliver the display panel gray scalevoltages matching with display data and more particularly to, a displayapparatus using liquid crystal, organic EL, plasma or the like and adriving device for displaying adapted for use in the same.

JP-A-6-348235 discloses a liquid crystal panel having X-signal lines andY-signal lines, a horizontal driver for selecting, on the basis of adata signal of an image to be displayed, one gray scale signal from aplurality of gray scale signals deliver out of a gray scale voltagegenerating circuit and delivering the selected gray scale voltage to anX-signal line of the liquid crystal panel, and a vertical driver fordelivering a scanning signal of the liquid crystal panel to a Y-signalline of the liquid crystal panel. It further discloses that the grayscale voltage generating circuit has a plurality of fixed resistorsconnected in series between a high-potential reference voltage and alow-potential reference voltage and voltage variable means for varyingvoltages at connection nodes of the fixed resistors between thehigh-potential and low-potential reference voltages. It furtherdiscloses that voltages at connection nodes of the fixed resistors aredelivered as gray scale signals. It further discloses that the voltagevariable means includes a variable resistor connected between thehigh-potential and low-potential reference voltages and an operationalamplifier having its one input terminal connected to a voltage variableterminal of the variable resistor and its output terminal connected to apredetermined connection node of the plurality of fixed resistors.

JP-A-10-142582 discloses that a resistor ladder circuit comprised ofresistors R0, R1, . . . , Rn and a resistor ladder circuit comprised ofresistors R0′, R1′, . . . Rn′ are connected between a power supplyterminal Vcc and a connection terminal GND, operational amplifiers OP1,OP2, . . . , OPn are connected between the two resistor ladder circuits,and a constant voltage generating circuit comprised of an operationalamplifier OP0 is connected to a node of the resistors Rn-1′ and Rn′. Itfurther discloses that output currents of the operational amplifiers OPnand OP1 are adjusted by the resistors Rn and R1 and an output current ofthe operational amplifier OP0 is adjusted by the resistor Rn′.

JP-A-2001-22325 discloses a liquid crystal display apparatus having avoltage division circuit for generating a plurality of positive-negativesymmetrical reference voltages from positive and negative referencevoltages, a variable voltage generating circuit for supplyingpositive-negative symmetrical reference voltages for gray scaleadjustment to one pair of positive-negative symmetrical voltage divisionpoints corresponding to a specified halftone of the voltage divisioncircuit, and one pair of amplifiers. It further discloses a liquidcrystal display apparatus having a voltage division circuit forgenerating a plurality of positive-negative symmetrical referencevoltages from positive and negative reference voltages, a plurality ofvariable voltage generating circuit for supplying positive-negativesymmetrical reference voltages for gray scale adjustment to a pluralityof pairs of positive-negative symmetrical voltage division pointscorresponding to a plurality of specified halftones of the voltagedivision circuit, and a plurality of differential amplifiers.

But none of the above prior arts take the following problems intoaccount.

Firstly, at the output of the gray scale voltage generating circuit,capacitive components including liquid crystal are charged/dischargedsimultaneously at a timing of A.C. (Alternating Current) operation. Forthe purpose of compensating the phase for an abrupt current change dueto the charge/discharge, it is general to connect a stabilizingcapacitor of 0.1 to 10 μF to the output of a voltage follower circuit.The stabilizing capacitor having a large capacitance as above needs tobe provided externally of an IC even when the gray scale voltagegenerating circuit is implemented in an IC form, thus increasing thenumber of parts. Secondly, in the liquid crystal display apparatus, withthe aim of preventing an image quality degradation similar to print,there needs a so-called A.C. operation for inverting, at a constantperiod, the polarity of a voltage applied to liquid crystal. In thisphase, through a so-called asymmetric drive method for instance thatmakes individual levels of gradation voltages different at the positiveand negative polarities, the amplitude of common voltage can be reducedand an image quality degradation such as flicker can be prevented toadvantage. To realize the asymmetric drive with the gray scale voltagegenerating circuit, the level of reference voltage may be different forthe positive and negative polarities. But, with the level of referencevoltage changed periodically, the stabilizing capacitor ischarged/discharged and as a result, consumption power increases.

Thirdly, in the liquid crystal display apparatus, an instance issupposed in which the number of colors possessed by input display datais smaller than the number of levels of generated gray scale voltages.In that case, unneeded gray scale voltages are generated by means of aladder resistor, with the result that a consumptive steady current flowsthrough the ladder resistor.

SUMMARY OF THE INVENTION

A first object of the invention is to provide a display apparatuscapable of reducing the number of parts by providing a voltage followercircuit dispensing with a stabilizing capacitor and to provide itsdriving device for displaying.

A second object of the invention is to provide a display apparatuscapable of avoiding an increase in consumption power by suppressingcharge/discharge current of a stabilizing capacitor during asymmetricdrive and to provide its driving device for displaying.

A third object of the invention is to provide a display apparatuscapable of suppressing an increase in consumption power by eliminating awaste of steady current flowing through a ladder resistor in match withthe number of display colors and to provide its driving device fordisplaying.

When the stabilizing capacitor is supposedly removed in the generalvoltage follower circuit, the most critical problem is that the phasemargin decreases, giving rise to a tendency to oscillation. To obviatethis problem, insertion of a resistor between the output of the voltagefollower circuit and a load is effective.

Accordingly, to accomplish the first object, a voltage follower circuitaccording to an aspect of the invention comprises a differentialamplifier, first and second buffer circuits, a resistor and twocompensating capacitors, wherein outputs of the first and second buffercircuits are connected to each other through a resistor, the output ofthe first buffer circuit is fed back to one input of the differentialamplifier and the output of the second buffer circuit serves as anoutput of the voltage follower circuit. By providing the resistorbetween the output of voltage follower circuit and a feedback point ofthe differential amplifier in this manner, the phase margin can beincreased and output operation can be stabilized. At the same time, theoutput of the second buffer circuit can directly drive the load, therebyensuring that the time constant can be decreased and the recovery timefrom voltage variations can be shortened.

To accomplish the second object, in a display apparatus according toanother embodiment of the invention, voltage follower circuits forpositive and negative polarities are provided and they are switched.With this construction, a potential applied to the stabilizing capacitorcan be constant even in asymmetric drive of the stabilizing capacitor tothereby suppress the charge/discharge.

To accomplish the third object, in a display apparatus according tostill another aspect of the invention, switches are provided whichseparate a ladder resistor at portions for generating unnecessary grayscale voltages or switch the ladder resistor to a high-resistanceresistor. With this construction, steady current flowing through theladder resistor can be optimized in match with the number of colorspossessed by display data to avoid an increase in consumption power.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the construction of a voltage followercircuit according to a first embodiment of the invention.

FIG. 2 is a circuit diagram showing the detailed construction of anexample of the voltage follower circuit in the first embodiment of theinvention.

FIG. 3 is a circuit diagram showing the detailed construction of anotherexample of the voltage follower circuit in the first embodiment of theinvention.

FIG. 4 is a circuit diagram showing the construction of a gray scalevoltage generating circuit in the first embodiment of the invention.

FIG. 5 is a block diagram showing the construction of a drain drivecircuit in the first embodiment of the invention.

FIG. 6 is a diagram useful to explain operation of the drain drivecircuit in the first embodiment of the invention.

FIG. 7 is a timing chart showing operation of the drain drive circuit inthe first embodiment of the invention.

FIG. 8 is a circuit diagram showing the construction of a gray scalevoltage generating circuit according to a second embodiment of theinvention.

FIG. 9 is a circuit diagram showing the construction of a gray scalevoltage generating circuit according to a third embodiment of theinvention.

FIG. 10 is a circuit diagram showing the construction of a gray scalevoltage generating circuit according to a fourth embodiment of theinvention.

FIG. 11 is a circuit diagram showing the construction of a gray scalevoltage generating circuit according to a fifth embodiment of theinvention.

FIG. 12 is a block diagram of an information processing apparatusprovided with the gray scale voltage generating circuit according to theinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates the fundamental construction of a voltage followercircuit according to a first embodiment of the invention. The voltagefollower circuit, as designated at reference numeral 101, in the presentembodiment comprises a differential amplifier 102, first and secondbuffer circuits 103 and 104, a resistor 105 and two compensatingcapacitances (for example, capacitors) 106 and 107. This circuitconstruction is featured in that outputs of the first and second buffercircuits 103 and 104 are connected to each other through the resistor105, with the output of first buffer circuit 103 being fed back to oneinput of the differential amplifier 102 and the output of the secondbuffer circuit 104 being connected to serve as an output of the voltagefollower circuit 101. By providing the resistor 105 between the outputof voltage follower circuit 101 and a node for feedback to thedifferential amplifier 102 in this manner, the phase margin can beincreased to stabilize output operation. In addition, since the outputof second buffer circuit 104 can directly drive a load, the timeconstant can be reduced and the recovery time from voltage variationscan be shortened. In other words, the first buffer circuit 103 has ahigh phase margin to function to prevent oscillation. The second buffercircuit 104 has a high through rate to function to reduce the feedbacktime.

The differential amplifier 102 receives at the other input an input fromthe outside of the voltage follower circuit 101 and, at one input, thefed back input. The output of differential amplifier 102 connects toground through the compensating capacitor 107. The first and secondbuffer circuits 103 and 104 receive the output of the differentialamplifier 102. The compensating capacitor 106 is connected in parallelwith the first buffer circuit 103. The output of the second buffercircuit 104 serves as the output of the voltage follower circuit 101.The output of first buffer circuit 103 and the output of second buffercircuit 104 routing through the resistor 105 are fed back to thedifferential amplifier 102.

The first embodiment of the invention will now be described withreference to FIGS. 2 to 7. The first embodiment of the invention isdirected to a voltage follower circuit dispensing with theaforementioned stabilizing capacitor, the detailed circuit constructionof which is exemplified in FIGS. 2 and 3.

In FIG. 2, a voltage follower circuit 201 comprises MOS transistors 202to 211, a resistor 212 and compensating capacitances (for example,capacitors) 213 and 214. For the correspondence with components of FIG.1, it will be appreciated that the differential amplifier 102corresponds to a component constituted by the MOS transistors 202 to205, the first buffer circuit 103 corresponds to a component constitutedby the MOS transistor 206 and the second buffer circuit 104 correspondsto a component constituted by the MOS transistors 207 to 211.

A voltage follower circuit 301 shown in FIG. 3 differs from the voltagefollower circuit 201 shown in FIG. 2 in that interchange of P channelwith N channel of the MOS transistors and interchange of connection ofpower supply voltage are carried out.

When considering the range of available voltage level, the voltagefollower circuit 201 has the output range close to ground voltage GND(low voltage) and the voltage follower circuit 301 has the output rangeclose to power supply voltage VDV (high voltage). Accordingly, it isdesirable that the two circuits be used purposively in accordance withthe level of a gray scale voltage to be delivered. A voltage followercircuit with stabilizing capacitor based on a so-called class “A”amplifier has a wider output range than that of the voltage followercircuit of the present invention. Therefore, for only a gray scalevoltage at a level close to the power supply voltage VDD or groundvoltage GND, the voltage follower circuit with stabilizing capacitor maybe used.

An example of the circuit construction based on this idea and used forgenerating 64 kinds of gray scale voltages will be described.

FIG. 4 is a circuit diagram showing the construction of a gray scalevoltage generating circuit 401. Comprises voltage follower circuits withstabilizing capacitors 402, 403 and 408, 409 based on so-called class“A” amplifiers, voltage follower circuits 404, 405 each implemented withthe aforementioned voltage follower circuit 301 according to the presentembodiment and voltage follower circuits 406, 407 each implemented withthe aforementioned voltage follower circuit 201 also according to thepresent embodiment. As will be seen from FIG. 4, the voltage followercircuits 402 to 409 are arranged in such a manner that the levels ofvoltages delivered out of these circuits become lower in this order.More particularly, the voltage level gradually decreases from thevoltage follower circuit 402 to the voltage follower circuit 409. Aladder resistor 410 divides outputs of the voltage follower circuits 402to 409 to generate gray scale voltages V0 to V63. In the gray scalevoltage generating circuit 401 of the present invention, referencevoltages, generally designated at Vref, are not inputted externally butare generated by inputting a 2-level reference voltage of referencevoltage VH at a high level and reference voltage VL at a low level anddividing the 2-level reference voltage by a ladder resistor 411.Advantageously, this can reduce the number of wiring lines leading tothe outside. With the circuit construction described above, the grayscale voltage generating circuit 401 can generate 64 kinds of gray scalevoltages. In each of the voltage follower circuits with stabilizingcapacitor 402, 403, 408 and 409, the differential amplifier has itsoutput fed back to its input. The output of the differential amplifieris connected on the other hand to ground through a stabilizingcapacitance 412 (for example, capacitor).

Next, construction and operation of a drain drive circuit including thegray scale voltage generating circuit 401 will be described by taking aninstance where so-called Vcom modulation drive s carried out.

FIG. 5 is a block diagram of the drain drive circuit designated at 501.The circuit 501 comprises a data latch circuit 502 for latching displaydata for one line, a data inversion circuit 503 for inverting thepolarity of the display data, and gray scale voltage selecting circuits504 each adapted to select a gray scale voltage matching with the datafrom a plurality of gray scale voltages V0 to V63 generated by the grayscale voltage generating circuit 401. Firstly, the drain drive circuit501 receives from an external liquid crystal controller a signal of CL1indicative of one scanning period (one horizontal period), a signal ofEN indicative of a period for transfer of effective display data, asignal of M indicative of the polarity of alternation (making italternate), a signal of CL2 indicative of a transfer clock of thedisplay data and a signal of DATA indicative of the display data. In thepresent embodiment, it is assumed that the DATA has gray scaleinformation of plural bits (for example, 6 bits) in respect of eachpixel.

FIG. 6 shows an example of operation of the drain drive circuit 501. Thedata latch circuit 502 repeats an operation in which it stores DATA forone line during a period of the EN being high (=1) by using the CL2 asfetching clock and delivers, as LD (line data), the stored DATA at atime in synchronism with the CL1. The data inversion circuit 503receives inputs of the LD and M and delivers a PD while keeping the LDunchanged when the M is at low level (=0) or after inverting the LD whenthe M is at high level (=1). Each of the gray scale voltage selectingcircuits 504 selects one gray scale voltage from the inputted gray scalevoltages V0 to V63 in accordance with a value of the PD so as to delivera VD.

FIG. 7 shows a timing chart useful to sum up the operation of the draindrive circuit 501. As will be seen from FIG. 7, voltage levels matchingwith the display data are delivered in accordance with the CL1, thusrealizing driving waveforms of general Vcom modulation drive.

The drain drive circuit 501 described herein was made in the form of anIC and actual characteristics were measured. Firstly, as for the outputrange, the voltage follower circuits 404 and 405 of the invention had(VDD−0.6V) or less and the voltage follower circuit 406 and 407 of theembodiment had (GND+0.8V) or more. In addition, when a 2-inch TFT liquidcrystal device of 120×160 pixels was connected to the drive circuit tocarry out the Vcom modulation drive at a frame frequency of 60 Hz, allgray scale voltages can be freed from adversity such as oscillation andan excellent display can be obtained.

As will be seen from the above, the voltage follower circuits 404 to 407of the present embodiment can provide good characteristics even withoutresort to the stabilizing capacitor 412 and therefore, in comparisonwith the conventional drain drive circuit, can reduce the number ofparts of stabilizing capacitor. In the gray scale voltage generatingcircuit 401 in the present embodiment, the voltage follower circuitswith stabilizing capacitor are used in combination but this constructionis not limitative. For example, if the ranges close to the power supplyvoltage VDD and the ground voltage GND are not used, the circuit may beconstructed of only the voltage follower circuits 201 and 301 in thepresent embodiment.

Next, other embodiments of the invention will be described withreference to FIGS. 8 to 10. In other embodiments, gray scale voltagegenerating circuits are provided which can realize suppression ofcharge/discharge of a stabilizing capacitor during asymmetrical drive.Like the foregoing, voltage follower circuits for positive and negativepolarities are provided and they are used in switching fashion.

FIG. 8 illustrates a circuit diagram showing the construction of a grayscale voltage generating circuit according to a second embodiment of theinvention. The circuit comprises switches for switching gray scalevoltages for positive and negative polarities, a ladder resistor 803 forgenerating gray scale voltages for positive polarity, and a ladderresistor 804 for generating gray scale voltages for negative polarity.Other components are identical to those of the gray scale voltagegenerating circuit 401 shown in FIG. 4. This circuit construction isfeatured in that there are provided two kinds of ladder resistors 803and 804 for positive and negative polarities and two kinds of voltagefollower circuits 402 and 408 for positive polarity and voltage followercircuits 403 and 409 for negative polarity and that switches areprovided which respond to an A.C. signal from the liquid crystalcontroller to switch the two kinds of ladder resistors and the two kindsof voltage follower circuits. In connection with the voltage followercircuits 402, 403 and 408, 409, outputs of these circuits are switchedby means of the switches. The switches 801 succeed the voltage followercircuits with stabilizing capacitors 402, 403 and 408, 409 whereas theswitches 802 precede voltage follower circuits without stabilizingcapacitors 404 to 407 in this embodiment. For example, during a periodfor the A.C. signal to be low (=0), the switch 801 selects a referencevoltage obtained by dividing a potential difference between referencevoltages VHP and VLP by means of the ladder resistor 803 for positivepolarity and during a period for the A.C. signal to be high (=1),selects a reference voltage obtained by dividing a potential differencebetween reference voltages VHN and VLN by means of the ladder resistor804 for negative polarity. With this construction, the outputs of thevoltage follower circuits 402, 403 and 408, 409 can be unvarying andcharge/discharge of the stabilizing capacitor 412 can be avoided. On theother hand, for the voltage follower circuits 404 to 407 dispensing withstabilizing capacitor in this embodiment, the switches 802 precedeamplifier inputs. This is because the number of amplifiers to be usedcan be decreased in comparison with the construction in which theamplifier input is followed by the switch. Like the foregoing, during aperiod for the A.C. signal to be low (=0), the switch 802 selects areference voltage obtained by dividing a potential difference betweenreference voltages VHP and VLP by means of the ladder resistor 803 forpositive polarity and during a period for the A.C. signal to be high(=1), selects a reference voltage obtained by dividing a potentialdifference between reference voltages VHN and VLN by means of the ladderresistor 804 for negative polarity.

FIG. 9 illustrates a circuit diagram showing the construction of a grayscale voltage generating circuit according to a third embodiment of theinvention. The circuit comprises switches 901 each adapted toselectively switch connection between a voltage follower circuit and twostabilizing capacitors 412 and switches 902 each adapted to make achoice of a reference voltage generated by a ladder resistor forpositive polarity or a reference voltage generated by a ladder resistorfor negative polarity. It will be seen from FIG. 9 that with thiscircuit construction, only the stabilizing capacitors 412 are providedfor positive and negative polarities and the switch is provided whichselectively switches connection of each of the voltage follower circuits402, 403 and 408, 409 to each of the stabilizing capacitors. Thisconstruction is advantageous over the gray scale voltage generatingcircuit in the second embodiment shown in FIG. 8 in that the number ofthe voltage follower circuits 402, 403 and 408, 409 can be one for onereference voltage to reduce the circuit scale. The switches 902 precedethe voltage follower circuits. The switch 901 selects one, for positivepolarity, of the two stabilizing capacitors 412 during a period for theA.C. signal to be low (=0) and selects the other, for negative polarity,of the two stabilizing capacitors during a period for the A.C. signal tobe high (=1).

FIG. 10 illustrates a circuit diagram showing the construction of a grayscale voltage generating circuit according to a fourth embodiment of theinvention. The circuit comprises resistors 1001 for positive polarity,resistors 1002 for negative polarity, and switches 1003 each adapted toselectively switch connection between a ladder resistor for generationof reference voltages and each of the resistors 1001 and 1002 forpositive and negative polarities. The circuit construction shown in FIG.10 intends to singularize the ladder resistor for generation ofreference voltages. Specifically, any one of the ladder resistors 803and 804 in the gray scale voltage generating circuit shown in FIG. 8 canbe unneeded. Namely, by making resistance of the resistor 1001 differentfrom that of the resistor 1002, gray scale voltages at different levelscan be generated at positive and negative polarities. This constructionis preferably applied to upper and lower ends of the ladder resistor soas to enhance the degree of freedom of adjustment. The switch 1003selects the resistor 1001 for positive polarity during a period for theA.C. signal to be low (=0) and selects the resistor 1002 for negativepolarity during a period for the A.C. signal to be high (=1).

In the gray scale voltage generating circuits according to the second tofourth embodiments of the invention set forth so far, even when theso-called asymmetric drive is carried out, charge/discharge of thestabilizing capacitor connected to the voltage follower circuit can beavoided. Accordingly, a drain drive circuit of more reduced consumptionpower can be provided.

FIG. 11 illustrates a circuit diagram showing the construction of a grayscale voltage generating circuit according to a fifth embodiment of theinvention. In the fifth embodiment of the invention, a method isdisclosed which can optimize steady current flowing through a ladderresistor in match with the number of colors possessed by display datawith the aim of eliminating any consumptive steady current flowing thethrough the ladder resistor. In the fifth embodiment, color numberinformation possessed by display data is of multiple bits (for example,plural bits amounting to 6 bits) or is of minor bits (for example, asingle bit amounting to one bit) and it is assumed that either state isdetermined by information supplied from the external liquid crystalcontroller. It is also assumed that when the color number informationpossessed by the display data is of 6 bits, all of 64 kinds of grayscale voltages (V0 to V63) are used and in case of one bit, only grayscale voltages at opposite ends (V0 and V63) are used.

The circuit of FIG. 11 comprises resistors 1101 for 6 bits, resistors1102 for one bit, and switches 1103 each adapted to switch connection tothe resistor 1101 for 6 bits and connection to the resistor 1102 for onebit in accordance with the color number information. For example, whenthe color number information is high (=1), the switch 1103 recognizes a6-bit display mode to select the resistor 1101 for 6 bits and when thecolor number information is low (=0), it recognizes a one-bit displaymode to select the resistor 1102 for one bit. Here, the resistance ofthe one-bit display resistor 1102 is so determined in advance as to besufficiently larger than that of the 6-bit resistor 1101 in order thatwhen the resistor 1102 is selected, the current flowing through theladder resistor can be reduced. This takes advantage of the fact that inthe display mode of the color number being one bit, only the gray scalevoltages at opposite ends (V0 and V63) are used as described previouslyand consequently, even if the levels of other gray scale voltages vary,this variation does not affect display. In case the display data is ofminor bits, the number of gray scales of the display data is small butin case the display data is of multiple bits, the number of gray scalesof the display data is large. In place of the resistor 1101 for 6 bits,resistor 1102 for one bit and switch 1103, a variable resistor can beused and in place of the switch 1103, a variable resistor controlcircuit can be used. For example, if the color number information ishigh (=1), the variable resistor control circuit recognizes the 6-bitdisplay mode to decrease the resistance of the variable resistor and ifthe color number information is low (=0), it recognizes the one-bitdisplay mode to increase the resistance of the variable resistor.

As described above, the gray scale voltage generating circuit accordingto the fifth embodiment of the invention can control the value ofcurrent flowing through the ladder resistor for generation of gray scalevoltages in accordance with the color number information. Accordingly, adrain drive circuit of more reduced consumption power can be provided.In the fifth embodiment of the invention, two kinds of resistors for 6bits and one bit are provided but this is not limitative and forexample, in the one-bit display mode, V0 and V63 can be completelydisconnected from the ladder resistor.

Thus, in an application of the gray scale voltage generating circuitaccording to the fifth embodiment of the invention to a handy phone oran information processing apparatus requiring low power such as PDA,when the information processing apparatus is in waiting condition, theMPU of the information processing apparatus may command informationpurporting that the number of colors is small to the gray scale voltagegenerating circuit and when the information processing apparatus is incall condition (during communication), the MPU of the informationprocessing apparatus may command information purporting that the numberof colors is large to the gray scale voltage generating circuit. Inother words, the information processing apparatus gives a display ofmultiple gray scale when the user makes use of it but gives a display ofminor gray scale when the user does not make use of it. Through this,power consumption in the gray scale voltage generating circuit can bereduced when the user does not make use of it, thus reducing powerconsumption in the information processing apparatus.

FIG. 12 illustrates a block diagram of an information processingapparatus provided with the gray scale voltage generating circuitaccording to the invention. The information processing apparatus, asgenerally designated at reference numeral 1, comprises a displayapparatus 2 for displaying display data and a MPU 3 for performingoperation processing. The display apparatus 2 includes a display panel 4having display pixels arranged in matrix, a drain drive circuit 501 forgenerating gray scale voltages corresponding to the display data andapplying the gray scale voltages to the display panel 4, a gate drivecircuit 5 for selecting a line of pixels to be applied with the grayscale voltages, and a system power supply generating circuit 6 forgenerating operating power supply for the drain drive circuit 501 andgate drive circuit 5. The system power supply generating circuit 6generates reference voltages VH, VL, VHP, VLH, VHN and VLN and a powersupply voltage VDD for the drain drive circuit 501. The drain drivecircuit 501 includes a gray scale voltage generating circuit 401 forgenerating a plurality of gray scale voltages V0 to V63, a gray scalevoltage selecting circuit 504 for selecting one gray scale voltagematched with the display data from the plurality of gray scale voltagesV0 to V63, a system interface 505 for receiving the display data andcontrol signals from the MPU 3, a display memory 506 (for example, RAM)for temporarily storing one frame of the display data, and a controlregister 507 for setting gray scale voltage characteristics matchingwith characteristics of the display panel 4. The control register 507includes a register for adjusting the amplitude, a register foradjusting the gradient and a register for performing fine adjustment, inthe relation between gray scale number and gray scale voltage.

The first to fifth embodiments of the invention have been described byway of example of the Vcom modulation drive but this is not limitativeand the invention may also be applied, on the basis of a similar idea,to dot inversion drive and column inversion drive known as other drivemethods.

Advantageously, the drain drive circuit according to the invention canreduce the number of external stabilizing capacitors used or dispensewith the external stabilizing capacitor to thereby attain costreduction. Further, even when external stabilizing capacitors areprovided, the circuit can be so constructed as to prevent thestabilizing capacitor per se from being charged/discharged andconsequently, consumption power can be reduced. Further, the necessarysteady current can be controlled in match with the number of colorspossessed by input display data, thereby making it possible to furtherreduce consumption power.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A display drive circuit for outputting a gray scale voltage accordingto display data to a display panel, comprising: a generation circuitwhich generates gray scale voltages of a plurality of levels; and aselection circuit which selects said gray scale voltage according tosaid display data, among gray scale voltages having said plurality oflevels; said display drive circuit having a one-bit mode in which thenumber of colors to be displayed on said display panel is small and amulti-bit mode in which the number of colors to be displayed on saiddisplay panel is large; wherein said generation circuit comprises afirst resistor for dividing a reference voltage and a second resistorfor further dividing the reference voltage divided by said firstresistor to generate said gray scale voltages of a plurality of levels,and a voltage follower circuit coupled between said first resistor andsaid second resistor; wherein said generation circuit, in said one-bitmode, decreases a current flowing into an internal circuit whichgenerates a gray scale voltage of an intermediate level other than twogray scale voltages of a gray scale voltage of the most lowest level anda gray scale voltage of the most highest level among the gray scalevoltages of said plurality of levels, said gray scale voltage of anintermediately level being free from affecting display; and wherein saidselection circuit, in said one-bit mode, selects said gray scale voltageaccording to said display data, from gray scale voltages of a pluralityof levels including said lowest level gray scale voltage, said highestlevel gray scale voltage and said intermediate level gray scale voltagewhich are generated from said generation circuit.
 2. A display drivecircuit according to claim 1, further comprising: a switching circuitwhich switches a resistance of a resistor for dividing between saidlowest level gray scale voltage and said intermediate level gray scalevoltage and a resistance of a resistor for dividing between said highestlevel gray scale voltage and said intermediate level gray scale voltagewith each other; wherein said switching circuit, in said one-bit mode,increases the resistance of said resistor for dividing between saidlowest level gray scale voltage and said intermediate level gray scalevoltage and the resistance of said resistor for dividing between saidhighest level gray scale voltage and said intermediate level gray scalevoltage.
 3. A display drive circuit according to claim 2, wherein saidresistor for dividing between said lowest level gray scale voltage andsaid intermediate level gray scale voltage further includes a resistorof a high resistance and another resistor of a low resistance connectedin parallel with each other; wherein said resistor for dividing betweensaid highest level gray scale voltage and said intermediate level grayscale voltage further includes a resistor of a high resistance andanother resistor of a low resistance connected in parallel with eachother; and wherein said switching circuit, in said one-bit mode, selectsa resistor of the high resistance resistor among the resistors fordividing between said lowest level gray scale voltage and saidintermediate level gray scale voltage, and selects a resistor of thehigh resistance among the resistors for dividing between said highestlevel gray scale voltage and said intermediate level gray scale voltage.4. A display drive circuit according to claim 2, wherein said resistorfor dividing between said lowest level gray scale voltage and saidintermediate level gray scale voltage and said resistor for dividingbetween said highest level gray scale voltage and said intermediatelevel gray scale voltage both are variable resistors; and wherein saidswitching circuit, in said one-bit mode, increases the resistance of thevariable resistor for dividing between said lowest gray scale voltageand said intermediate level gray scale voltage and the resistance of thevariable resistor for dividing between said highest level gray scalevoltage and said intermediate gray scale voltage.
 5. A display drivecircuit for outputting a gray scale voltage according to display data toa display panel, comprising: a generation circuit which generates grayscale voltages of 64 levels from 0-th level to 63-th level; and aselection circuit which selects said gray scale voltage according tosaid display data, among gray scale voltages having said 64 levels; saiddisplay drive circuit having a one-bit mode in which the number ofcolors to be displayed on said display panel is small and a multi-bitmode in which the number of colors to be displayed on said display panelis large; wherein said generation circuit comprises a first resistor fordividing a reference voltage and a second resistor for further dividingthe reference voltage divided by said first resistor to generate saidgray scale voltages of a plurality of levels, and a voltage followercircuit coupled between said first resistor and said second resistor;wherein said generation circuit, in said one-bit mode, decreases acurrent flowing into an internal circuit which generates a gray scalevoltage from the first level to 62-th level other than two gray scalevoltages of a gray scale voltage of the 0-th level and a gray scalevoltage of the 63-th level among the gray scale voltages of said 64levels said gray scale voltage of from the first level to 62-th levelbeing free from affecting display; wherein said selection circuit, insaid one-bit mode, selects said gray scale voltage according to saiddisplay data, from the two gray scale voltages of said 0-th level grayscale voltage and said 63-th level gray scale voltage which aregenerated from said generation; and wherein said selection circuit, insaid multi-bit mode, selects said gray scale voltage according to saiddisplay data, from gray scale voltages of 64 levels of from said 0-thlevel gray scale voltage to said 63-th level gray scale voltage.
 6. Adisplay drive circuit according to claim 5, further comprising aswitching circuit for switching between a resistance of a resistordividing between said 0-th level gray scale voltage and the gray scalevoltages of from said first level to said 62-th level and a resistanceof another resistor dividing between said first to 62-th level grayscale voltages and said 63-th level gray scale voltage, wherein saidswitching circuit, in said one-bit mode, sets to be large saidresistance of a resistor dividing between said 0-th level gray scalevoltage and the gray scale voltages of from said first level to said62-th level and said resistance of another resistor dividing betweensaid first to 62-th level gray scale voltages and said 63-th level grayscale voltage.
 7. A display drive circuit according to claim 6, whereinsaid resistor, dividing between said 0-th level gray scale voltage andthe gray scale voltages of from said first level to said 62-th levelfurther comprises a high-resistance resistor and a low-resistanceresistor connected in parallel with each other, said another resistordividing between said first to 62-th level gray scale voltages and said63-th level gray scale voltage further comprises a high-resistanceresistor and a low-resistance resistor connected in parallel with eachother, and said switching circuit, in said one-bit mode, selects thehigh-resistance resistor among said resistor dividing between said 0-thlevel gray scale voltage and the gray scale voltages of from said firstlevel to said 62-th level and selects the high-resistance resistor amongsaid another resistor dividing between said first to 62-th level grayscale voltages and said 63-th level gray scale voltage.
 8. A displaydrive circuit according to claim 6, wherein said resistor dividingbetween said 0-th level gray scale voltage and the gray scale voltagesof from said first level to said 62-th level and said another resistordividing between said first to 62-th level gray scale voltages and said63-th level gray scale voltage are formed variable resistors, saidswitching circuit, in said one-bit mode, sets to be large said variableresistor dividing between said 0-th level gray scale voltage and thegray scale voltages of from said first level to said 62-th level andsaid another variable resistor dividing between said first to 62-thlevel gray scale voltages and said 63-th level gray scale voltage.
 9. Adisplay drive circuit for outputting a gray scale voltage according todisplay data to a display panel, comprising: a generation circuit whichgenerates gray scale voltages of a plurality of levels; and a selectioncircuit which selects said gray scale voltage according to said displaydata, among gray scale voltages having said plurality of levels; saiddisplay drive circuit having a one-bit mode in which the number ofcolors to be displayed on said display panel is small and a multi-bitmode in which the number of colors to be displayed on said display panelis large; wherein said generation circuit comprises a first resistor fordividing a reference voltage and a second resistor for further dividingthe reference voltage divided by said first resistor to generate saidgray scale voltage of a plurality of levels, and a voltage followercircuit coupled between said first resistor and said second resistor;wherein said generation circuit, in said one-bit mode, decreases acurrent flowing into an internal circuit which generates a gray scalevoltage of an intermediate level other than two gray scale voltages of agray scale voltage of the most lowest level and a gray scale voltage ofthe most highest level among the gray scale voltages of said pluralityof levels, said gray scale voltage of an intermediate level being freefrom affecting display; wherein said selection circuit, in said one-bitmode, selects said gray scale voltage according to said display data,from the two gray scale voltages of said most lowest level gray scalevoltage and said most highest level gray scale voltage which aregenerated from said generation circuit; wherein said selection circuit,in said multi-bit mode, selects said gray scale voltage according tosaid display data, from gray scale voltages of a plurality of levelsincluding said low level gray scale voltage, said high level gray scalevoltage and said intermediate level gray scale voltage which aregenerated from said generation circuit; wherein an external MPU(microprocessor unit) judges whether or not said number of colors to bedisplayed on the display panel is small; and wherein said display drivecircuit receives information representing either of said one-bit modeand said multi-bit mode, from said external MPU.
 10. A display drivecircuit according to claim 9, further comprising a switching circuit forswitching between a resistance of a resistor dividing between said lowlevel gray scale voltage and said intermediate level gray scale voltageand a resistance of another resistor dividing between said intermediatelevel gray scale voltages and said high level gray scale voltage,wherein said switching circuit, in said one-bit mode, sets to be largesaid resistance of a resistor dividing between said low level gray scalevoltage and said intermediate level gray scale voltage and said anotherresistor dividing between said intermediate level gray scale voltage andsaid high level gray scale voltage.
 11. A display drive circuitaccording to claim 10, wherein said resistor dividing between said lowlevel gray scale voltage and said intermediate level gray scale voltagefurther comprises a high-resistance resistor and a low-resistanceresistor connected in parallel with each other, said another resistordividing between said intermediate level gray scale voltage and saidhigh level gray scale voltage further comprises a high-resistanceresistor and a low-resistance resistor connected in parallel with eachother, and said switching circuit, in said one-bit mode, selects thehigh-resistance resistor among said resistor dividing between said lowlevel gray scale voltage and said intermediate level gray scale voltage,and selects the high-resistance resistor among said another resistordividing between said intermediate level gray scale voltage and saidhigh level gray scale voltage.
 12. A display drive circuit according toclaim 10, wherein said resistor dividing between said low level grayscale voltage and said intermediate level gray scale voltage and saidanother resistor dividing between said intermediate level gray scalevoltage and said high level gray scale voltage are formed of variableresistors, said switching circuit, in said one-bit mode, sets to belarge said variable resistor dividing between said low level gray scalevoltage and said intermediate level gray scale voltage and said anothervariable resistor dividing between said intermediate level gray scalevoltage and said high level gray scale voltage.
 13. A display drivecircuit for outputting a gray scale voltage according to display data toa display panel, comprising: a system interface for inputting said dataexternally; a memory for storing display data; a generation circuitwhich generates gray scale voltages of plurality of levels; a selectioncircuit which selects said gray scale voltage according to said displaydata from said memory, among gray scale voltages having said pluralityof levels; a gradient adjusting register for adjusting a gradient of agray scale voltage characteristic; an amplitude adjusting register foradjusting an amplitude of said gray scale voltage characteristic; and afine adjusting register for a fine-adjusting said gray scale voltagecharacteristic; said display drive circuit having a one-bit mode inwhich the number of colors to be displayed on said display panel issmall and a multi-bit mode in which the number of colors to be displayedon said display panel is large; wherein said generation circuitcomprises a first resistor for dividing a reference voltage and a secondresistor for further dividing the reference voltage divided by saidfirst resistor to generate said gray scale voltages of a plurality oflevels, and a voltage follower circuit coupled between said firstresistor and said second resistor; wherein said generation circuit, insaid one-bit mode, decreases a current flowing into an internal circuitwhich generates a gray scale voltage of a level other than two grayscale voltages of a gray scale voltage of a first level and a gray scalevoltage of a second level among the gray scale voltages of saidplurality of levels, said other level gray scale voltage being free fromaffecting display; wherein said selection circuit, in said one-bit mode,selects said gray scale voltage according to said display data, from thetwo gray scale voltages of said first level gray scale voltage and saidsecond level gray scale voltage which are generated from said generationcircuit; and wherein said selection circuit, in said multi-bit mode,selects said gray scale voltage according to said display data, fromgray scale voltages of a plurality of levels including said first levelgray scale voltage, said second level gray scale voltage and said otherlevel gray scale voltage which are generated from said generationcircuit.
 14. A display drive circuit according to claim 13, furthercomprising a switching circuit for switching between a resistance of aresistor dividing between said first level gray scale voltage and saidother level gray scale voltage and a resistance of another resistordividing between said other level gray scale voltages and said secondlevel gray scale voltage, wherein said switching circuit, in saidone-bit mode, sets to be large said resistance of a resistor dividingbetween said first level gray scale voltage and said other level grayscale voltage and said another resistor dividing between said otherlevel gray scale voltage and said second level gray scale voltage.
 15. Adisplay drive circuit according to claim 14, wherein said resistordividing between said first level gray scale voltage and said otherlevel gray scale voltage further comprises a high-resistance resistorand a low-resistance resistor connected in parallel with each other,said another resistor dividing between said other level gray scalevoltage and said second level gray scale voltage further comprises ahigh-resistance resistor and a low-resistance resistor connected inparallel with each other, and said switching circuit, in said one-bitmode, selects the high-resistance resistor among said resistor dividingbetween said first level gray scale voltage and said other level grayscale voltage, and selects the high-resistance resistor among saidanother resistor dividing between said other level gray scale voltageand said second level gray scale voltage.
 16. A display drive circuitaccording to claim 14, wherein said resistor dividing between said firstlevel gray scale voltage and said other level gray scale voltage andsaid another resistor dividing between said other level gray scalevoltage and said second level gray scale voltage are formed of variableresistors, said switching circuit, in said one-bit mode, sets to belarge said variable resistor dividing between said first level grayscale voltage and said other level gray scale voltage and said anothervariable resistor dividing between said other level gray scale voltageand said second level gray scale voltage.
 17. A display drive circuitfor outputting a gray scale voltage according to display data to adisplay panel, comprising: a generation circuit which generates grayscale voltages of a plurality of levels; and a selection circuit whichselects said gray scale voltage according to said display data, amonggray scale voltages having said plurality of levels; said display drivecircuit having a one-bit mode in which the number of colors to bedisplayed on said display panel is small and a multi-bit mode in whichthe number of colors to be displayed on said display panel is large;wherein said generation circuit comprises a first resistor for dividinga reference voltage and a second resistor for further dividing thereference voltage divided by said first resistor to generate said grayscale voltages of a plurality of levels, and a voltage follower circuitcoupled between said first resistor and said second resistor; whereinsaid generation circuit, in said one-bit mode, disconnects an internalcircuit which generates a gray scale voltage of an intermediate levelother than two gray scale voltages of a gray scale voltage of the mostlowest level and a gray scale voltage of the most highest level amongthe gray scale voltages of said plurality of levels, said intermediatelevel gray scale voltage being free from affecting display; wherein saidselection circuit, in said one-bit mode, selects said gray scale voltageaccording to said display data, from the two gray scale voltages of saidmost lowest level of said gray scale voltage and said most highest levelgray scale voltage which are generated from said generation; and whereinsaid selection circuit, in said multi-bit mode, selects said gray scalevoltage according to said display data, from gray scale voltages of aplurality of levels including said most lowest level gray scale voltage,said most highest level gray scale voltage and said intermediate levelgray scale voltage which are generated from said generation circuit. 18.A display drive circuit according to claim 17, further comprising: aswitching circuit which switches a resistance of a resistor for dividingbetween said lowest level gray scale voltage and said intermediate levelgray scale voltage and a resistance of a resistor for dividing betweensaid highest level gray scale voltage and said intermediate level grayscale voltage with each other; wherein said switching circuit, in saidone bit mode, increases the resistance of said resistor for dividingbetween said lowest level gray scale voltage and said intermediate levelgray scale voltage and the resistance of said resistor for dividingbetween said highest level gray scale voltage and said intermediatelevel gray scale voltage.
 19. A display drive circuit according to claim18, wherein said resistor for dividing between said lowest level grayscale voltage and said intermediate level gray scale voltage furtherincludes a resistor of a high resistance and another resistor of a lowresistance connected in parallel with each other; wherein said resistorfor dividing between said highest level gray scale voltage and saidintermediate level gray scale voltage further includes a resistor of ahigh resistance and another resistor of a low resistance connected inparallel with each other; and wherein a switching circuit, in saidone-bit mode, selects a resistor of the high resistance resistor amongthe resistors for dividing between said lowest level gray scale voltageand said intermediate level gray scale voltage, and selects a resistorof the high resistance among the resistors for dividing between saidhighest level gray scale voltage and said intermediate level gray scalevoltage.
 20. A display drive circuit according to claim 19, wherein saidresistor for dividing between said lowest level gray scale voltage andsaid intermediate level gray scale voltage and said resistor fordividing between said highest level gray scale voltage and saidintermediate level gray scale voltage both are variable resistors; andwherein a switching circuit, in said one-bit mode, increases theresistance of variable resistor for dividing between said lowest levelgray scale voltage and said intermediate level gray scale voltage andthe resistance of variable resistor for dividing between said highestlevel gray scale voltage and said intermediate level gray scale voltage.21. A display drive circuit for outputting a gray scale voltageaccording to display data to a display panel, comprising: a generationcircuit which generates gray scale voltages of 64 levels from 0-th levelto 63-th level; and a selection circuit which selects said gray scalevoltage according to said display data, among gray scale voltages having64 levels; said display drive circuit having a one-bit mode in which thenumber of colors to be displayed on said display panel is small and amulti-bit mode in which the number of colors to be displayed on saiddisplay panel is large; wherein said generation circuit comprises afirst resistor for dividing a reference voltage and a second resistorfor further dividing the reference voltage divided by said firstresistor to generate said gray scale voltages of a plurality of levels,and a voltage follower circuit coupled between said first resistor andsaid second resistor; wherein said generation circuit, in said one-bitmode, disconnects an internal circuit which generates a gray scalevoltage of from the first level to 62-th level other than two gray scalevoltages of a gray scale voltage of the 0-th level and a gray scalevoltage of the 63-th level among the gray scale voltages of said 64levels, said gray scale voltage of from the first level to 62-th levelbeing free from affecting display; wherein said selection circuit,selects said gray scale voltage according to said display data, from thetwo gray scale voltages of said 0-th level gray scale voltage and said63-th level gray scale voltage which are generated from said generation;and wherein said selection circuit, in said multi-bit mode, selects saidgray scale voltage according to said display data, from gray scalevoltages of 64 levels of from said 0-th level gray scale voltage to said63-th level gray scale voltage which are generated from said generationcircuit.
 22. A display drive circuit according to claim 21, furthercomprising a switching circuit for switching between a resistance of aresistor dividing between said 0-th level gray scale voltage and thegray scale voltages of from said first level to said 62-th level and aresistance of another resistor dividing between said first to 62-thlevel gray scale voltages and said 63-th level gray scale voltage,wherein said switching circuit, in said one-bit mode, sets to be largesaid resistance of a resistor dividing between said 0-th level grayscale voltage and the gray scale voltages of from said first level tosaid 62-th level and said resistance of another resistor dividingbetween said first to 62-th level gray scale voltages and said 63-thlevel gray scale voltage.
 23. A display drive circuit according to claim22, wherein said resistor dividing between said 0-th level gray scalevoltage and the gray scale voltages of from said first level to said62-th level further comprises a high-resistance resistor and alow-resistance resistor connected in parallel with each other, saidanother resistor dividing between said first to 62-th level gray scalevoltages and said 63-th level gray scale voltage further comprises ahigh-resistance resistor and a low-resistance resistor connected inparallel with each other, and said switching circuit, in said non-bitmode, selects the high-resistance resistor among said resistor dividingbetween said 0-th level gray scale voltage and the gray scale voltagesof from said first level to said 62-th level and selects thehigh-resistance resistor among said another resistor dividing betweensaid first to 62-th level gray scale voltages and said 63-th level grayscale voltage.
 24. A display drive circuit according to claim 22,wherein said resistor dividing between said 0-th level gray scalevoltage and the gray scale voltages of from said first level to said62-th level and said another resistor dividing between said first to62-th level gray scale voltages and said 63-th level gray scale voltageare formed variable resistors, said switching circuit, in said one-bitmode, sets to be large said variable resistor dividing between said 0-thlevel gray scale voltage and the gray scale voltages of from said firstlevel to said 62-th level and said another variable resistor dividingbetween said first to 62-th level gray scale voltages and said 63-thlevel gray scale voltage.
 25. A display drive circuit for outputting agray scale voltage according to display data to a display panel,comprising: a generation circuit which generates gray scale voltages ofa plurality of levels; and a selection circuit which selects said grayscale voltage according to said data display, among gray scale voltageshaving said plurality of levels; said display drive circuit having aone-bit mode in which the number of colors to be displayed on saiddisplay panel is small and a multi-bit mode in which the number ofcolors to be displayed on said display panel is large; wherein saidgeneration circuit comprises a first resistor for dividing a referencevoltage and a second resistor for further dividing the reference voltagedivided by said first resistor to generate said gray scale voltages of aplurality of levels, and a voltage follower circuit coupled between saidfirst resistor and said second resistor; wherein said generationcircuit, in said one-bit mode, disconnects an internal circuit whichgenerates a gray scale voltage of an intermediate level other than twogray scale voltages of a gray scale voltage of a low level and a grayscale voltage of a high level among the gray scale voltages of saidplurality of levels, said intermediate level gray scale voltage beingfree from affecting display; wherein said selection circuit, in saidone-bit mode selects said gray scale voltage according to said displaydata, from the two gray scale voltages of said low level gray scalevoltage and said high level gray scale voltage which are generated fromsaid generation circuit; wherein said selection circuit, in saidmulti-bit mode, selects said gray scale voltage according to saiddisplay data, from gray scale voltages of a plurality of levelsincluding said low level gray scale voltage, said high level gray scalevoltage and said intermediate level gray scale voltage which aregenerated from said generation circuit; wherein an external MPU(microprocessor unit) judges whether or not said number of colors to bedisplayed on the display panel is small; and wherein said display drivecircuit receives information representing either of said one-bit modeand said multi-bit mode, from said external MPU.
 26. A display drivecircuit according to claim 25, further comprising a switching circuitfor switching between a resistance of a resistor dividing between saidlow level gray scale voltage and said intermediate level gray scalevoltage and a resistance of another resistor dividing between saidintermediate level gray scale voltages and said high level gray scalevoltage, wherein said switching circuit, in said one-bit mode, sets tobe large said resistance of a resistor dividing between said low levelgray scale voltage and said intermediate level gray scale voltage andsaid another resistor dividing between said intermediate level grayscale voltage and said high level gray scale voltage.
 27. A displaydrive circuit according to claim 26, wherein said resistor dividingbetween said low level gray scale voltage and said intermediate levelgray scale voltage further comprises a high-resistance resistor and alow-resistance resistor connected in parallel with each other, saidanother resistor dividing between said intermediate level gray scalevoltage and said high level gray scale voltage further comprises ahigh-resistance resistor and a low-resistance resistor connected inparallel with each other, and said switching circuit, in said one-bitmode, selects the high-resistance resistor among said resistor dividingbetween said low level gray scale voltage and said intermediate levelgray scale voltage, and selects the high-resistance resistor among saidanother resistor dividing between said intermediate level gray scalevoltage and said high level gray scale voltage.
 28. A display drivecircuit according to claim 26, wherein said resistor dividing betweensaid low level gray scale voltage and said intermediate level gray scalevoltage and said another resistor dividing between said intermediatelevel gray scale voltage and said high level gray scale voltage areformed of variable resistors, said switching circuit, in said one-bitmode, sets to be large said variable resistor dividing between said lowlevel gray scale voltage and said intermediate level gray scale voltageand said another variable resistor dividing between said intermediatelevel gray scale voltage and said high level gray scale voltage.
 29. Adisplay drive circuit for outputting a gray scale voltage according todisplay data to a display panel, comprising: a system interface forinputting said display data externally; a memory for storing saiddisplay data; a generation circuit which generates gray scale voltagesof a plurality of levels; a selection circuit which selects said grayscale voltage according to said display data from said memory, amonggray scale voltages having said plurality of levels; a gradientadjusting register for adjusting a gradient of a gray scale voltagecharacteristic; an amplitude adjusting register for adjusting anamplitude of said gray scale voltage characteristic; and a fineadjusting register for fine-adjusting said gray scale voltagecharacteristic; said display drive circuit having a one-bit mode inwhich the number of colors to be displayed on said display panel issmall and a multi-bit mode in which the number of colors to be displayedon said display panel is large; wherein said generation circuitcomprises a first resistor for dividing a reference voltage and a secondresistor for further dividing the reference voltage divided by saidfirst resistor to generate said gray scale voltages of a plurality oflevels, and a voltage follower circuit coupled between said firstresistor and said second resistor; wherein said generation circuit, insaid one-bit mode, disconnects an internal circuit which generates agray scale voltage of a level other than two gray scale voltages of agray scale voltage of a first level and a gray scale voltage of a secondlevel among the gray scale voltages of said plurality of levels, saidother level gray scale being free from affecting display; wherein saidselection circuit, in said one-bit mode, selects said gray scale voltageaccording to said display data, from the two gray scale voltages of saidfirst level gray scale voltage and said second level gray scale voltagewhich are generated from said generation; and wherein said selectioncircuit, in said multi-bit mode, selects said gray scale voltageaccording to said display data, from gray scale voltages of a pluralityof levels including said first level gray scale voltage, said secondlevel gray scale voltage and said intermediate level gray scale voltagewhich are generated from said generation circuit.
 30. A display drivecircuit according to claim 29, further comprising a switching circuitfor switching between a resistance of a resistor dividing between saidfirst level gray scale voltage and said other level gray scale voltageand a resistance of another resistor dividing between said other levelgray scale voltages and said second level gray scale voltage, whereinsaid switching circuit, in said one-bit mode, sets to be large saidresistance of a resistor dividing between said first level gray scalevoltage and said other level gray scale voltage and said anotherresistor dividing between said other level gray scale voltage and saidsecond level gray scale voltage.
 31. A display drive circuit accordingto claim 30, wherein said resistor dividing between said first levelgray scale voltage and said other level gray scale voltage furthercomprises a high-resistance resistor and a low-resistance resistorconnected in parallel with each other, said another resistor dividingbetween said other level gray scale voltage and said second level grayscale voltage further comprises a high-resistance resistor and alow-resistance resistor connected in parallel with each other, and saidswitching circuit, in said one-bit mode, selects the high-resistanceresistor among said resistor dividing between said first level grayscale voltage and said other level gray scale voltage, and selects thehigh-resistance resistor among said another resistor dividing betweensaid other level gray scale voltage and said second level gray scalevoltage.
 32. A display drive circuit according to claim 30, wherein saidresistor dividing between said first level gray scale voltage and saidother level gray scale voltage and said another resistor dividingbetween said other level gray scale voltage and said second level grayscale voltage are formed of variable resistors, said switching circuit,in said one-bit mode, sets to be large said variable resistor dividingbetween said first level gray scale voltage and said other level grayscale voltage and said another variable resistor dividing between saidother level gray scale voltage and said second level gray scale voltage.